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Abstract:

A real-time trigger figure-of-merit indicator for test and measurement
instruments provides an indication of how close a signal-under-test is to
satisfying a relevant trigger condition. The indicator includes a first
marker that indicates a real-time trigger figure-of-merit that is
calculated based on digital samples that represent the signal-under-test,
and a second marker that indicates a level that the figure-of-merit must
exceed in order for a trigger event detector to detect a trigger event
and generate a trigger signal. Thus, by observing the indicator, a user
may easily ascertain how close a signal-under-test is to satisfying the
relevant trigger condition without requiring the instrument to actually
trigger.

Claims:

1. A real-time trigger figure-of-merit indicator comprising: a first
marker that indicates a real-time trigger figure-of-merit that is
calculated based on digitized samples that represent a signal-under-test;
and a second marker that indicates a level that the figure-of-merit must
exceed in order for a trigger event detector to detect a trigger event
and generate a trigger signal.

2. A trigger figure-of-merit indicator as in claim 1 further comprising a
third marker that indicates a state of the trigger event detector.

3. A real-time trigger figure-of-merit indicator as in claim 1 wherein
the trigger event detector is selected from the group consisting of a
power level trigger, a filtered power level trigger, a frequency mask
trigger, a density trigger, a modulation domain trigger, an external
trigger, a data pattern trigger, and a spectral signature trigger.

4. A test and measurement instrument having a real-time trigger
figure-of-merit indicator according to claim 1.

5. A test and measurement instrument as in claim 4 wherein the test and
measurement instrument is a test and measurement instrument selected from
the group consisting of a spectrum analyzer, an oscilloscope, and a logic
analyzer.

6. A test and measurement instrument as in claim 4 wherein the real-time
trigger figure-of-merit indicator is displayed on a display means
selected from the group consisting of a display device and a front-panel.

Description:

FIELD OF THE INVENTION

[0001] The present invention relates to test and measurement instruments,
and more particularly to tools that make it easier for a user to set up
and arm a trigger event detector.

BACKGROUND OF THE INVENTION

[0002] Test and measurement instruments such as spectrum analyzers,
oscilloscopes, and logic analyzers have "trigger event detectors" that
allow them to capture and analyze portions of a signal-under-test before,
at, and after specific events occur referred to as "trigger events."
Trigger events can be detected from the signal-under-test itself or from
a secondary signal. In order to insure a high probability of detecting a
trigger event, a trigger event detector must operate continuously,
regardless of whether a trigger event is present or not. FIG. 1
illustrates a spectrum analyzer 100 having such a trigger event detector
105. In operation, a signal-under-test is conditioned by a signal
conditioner 110 (e.g., by down-converting the signal-under-test from RF
to IF) and then digitized by an analog-to-digital converter (ADC) 115 to
produce a continuous stream of digitized samples. The digitized samples
are written into a circular buffer 120 and also input to the trigger
event detector 105. The trigger event detector 105 processes the digital
samples and then compares the processed samples to a user-specified
trigger threshold. When the processed digital samples exceed the trigger
threshold, the trigger event generator 105 generates a trigger signal
that causes an acquisition memory 125 to capture the digitized samples
that are held in the circular buffer 120. The captured samples are then
analyzed by a display processor 130 (e.g., by transforming them into the
frequency domain using a frequency transform such as a fast Fourier
transform (FFT), a chirp-Z transform, or the like) and displayed on a
display device 135. The trigger event detector 105 may be any one of
various kinds of trigger event detectors that are used to detect various
kinds of trigger events. For example, the trigger event detector 105 may
be a "power level trigger" that detects when the instantaneous power of
the signal-under-test exceeds a user-specified power threshold. In that
case, the trigger event detector 105 processes the digitized samples by
converting them into a measure of the instantaneous power of the
signal-under-test, and the user-specified trigger threshold is a power
threshold. When the instantaneous power of the signal-under-test exceeds
the power threshold, the trigger event generator 105 generates the
trigger signal.

[0003] In order to detect more complex trigger events, a trigger event
detector may need to be more selective than the acquisition path of the
instrument (i.e., the signal conditioner, ADC, circular buffer,
acquisition memory, and so on). For example, as shown in FIG. 2, a
spectrum analyzer 200 may include a band-pass filter (BPF) 240 that
filters the signal-under-test before it is applied to the trigger event
detector 205 so that the trigger event detector 205 only detects trigger
events within a narrow range of frequencies (as described in U.S. Pat.
No. 5,493,209 titled "Tunable trigger acquisition system and method for
making in-service time-domain signal measurements"). In this manner, the
bandwidth of the signal received by the trigger event detector 205 is
much narrower than the bandwidth of the signal-under-test displayed on
the display device 235.

[0004] The deficiency in these conventional instruments is that it is
difficult for a user to ascertain how to set up and arm the trigger event
detector. That is, the user cannot see the signal-under-test on the
display device until a trigger event occurs. Thus, if the trigger event
detector is set up improperly or if the signal-under-test changes after
the user arms the trigger event detector, then the user has no way of
ascertaining why the instrument is not triggering. This deficiency is
particularly problematic in the case where the trigger event detector is
more selective than the acquisition path of the instrument because, even
if the user can somehow get the instrument to display the
signal-under-test (e.g., by forcing a trigger), the signal-under-test
shown on the display device does not necessarily correspond to the signal
received by the trigger event detector.

SUMMARY OF THE INVENTION

[0005] What is needed is a way for a user to easily ascertain how close a
signal-under-test is to satisfying a relevant trigger condition.

[0006] Accordingly, embodiments of the present invention provide a
real-time trigger figure-of-merit indicator for test and measurement
instruments that provides an indication of how close a signal-under-test
is to satisfying a relevant trigger condition. The indicator includes a
first marker that indicates a real-time trigger figure-of-merit that is
calculated based on digital samples that represent the signal-under-test,
and a second marker that indicates a level that the figure-of-merit must
exceed in order for a trigger event detector to detect a trigger event
and generate a trigger signal. Thus, by observing the indicator, a user
may easily ascertain how close a signal-under-test is to satisfying the
relevant trigger condition without requiring the instrument to actually
trigger.

[0007] The objects, advantages and other novel features of the present
invention are apparent from the following detailed description when read
in conjunction with the appended claims and attached drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 depicts a high-level block diagram of a conventional
spectrum analyzer having a power level trigger.

[0009] FIG. 2 depicts a high-level block diagram of a conventional
spectrum analyzer having a filtered power level trigger.

[0010]FIG. 3 depicts a high-level block diagram of a spectrum analyzer
having a real-time trigger figure-of-merit indicator according to an
embodiment of the present invention.

[0012] Referring now to FIG. 3, a spectrum analyzer 300 according to an
embodiment of the present invention is similar to the spectrum analyzer
100 shown in FIG. 1 but also includes a processor 345 that receives a
copy of the processed digital samples from the trigger event detector 305
and a copy of the user-specified trigger threshold, and generates based
on them a real-time trigger figure-of-merit indicator 350 that indicates
how close the signal-under-test is to satisfying a relevant trigger
condition. Referring now to FIG. 4, the indicator 350 includes a first
marker 455 that indicates a real-time trigger "figure-of-merit" that is
calculated based on the processed digital samples. For example, if the
trigger event detector 305 is a power level trigger, then the
figure-of-merit is the instantaneous power of the signal-under-test.
Similarly, if the trigger event detector 305 is a filtered power level
trigger, then the figure-of-merit is the instantaneous power of the
filtered signal-under-test. The indicator 350 also includes a second
marker 460 that indicates a level that the figure-of-merit must exceed in
order for the trigger event detector 305 to detect a trigger event and
generate a trigger signal. For example, if the trigger event detector 305
is a power level trigger or filtered power level trigger, then the marker
460 indicates the user-specified power threshold. Optionally, the
indicator 350 may also include a third marker 465 that indicates the
state of the trigger event detector 305, i.e., "armed", "ready",
"triggered," and so on. The indicator 350 may be displayed on the display
device 335, on a front-panel of the instrument (not shown), or in cases
where the instrument is controlled by a remote computer (not shown), the
indicator 350 may be displayed on a display device of that computer.
Thus, by simply observing the indicator 350, a user may easily ascertain
how close the signal-under-test is to satisfying a relevant trigger
condition. This is particularly advantageous for instruments in which the
trigger event detector is more selective than the acquisition path of the
instrument.

[0013] The real-time trigger figure-of-merit is not only useful when used
in conjunction with a power level trigger and a filtered power level
trigger, but in various other embodiments may be adapted to be used with
any type of trigger event detector. For example:

[0014] In another embodiment, the trigger event detector 305 is a
"frequency mask trigger" as described in U.S. Pat. No. 5,103,402 titled
"Method and apparatus for identifying, saving, and analyzing continuous
frequency domain data in a spectrum analyzer" which transforms the
digitized samples of the signal-under-test into a continuous series of
frequency spectra and generates a trigger signal when a frequency
spectrum violates a user-defined frequency mask. In that case, the
processed digital samples are the frequency spectra and the
user-specified trigger threshold is the frequency mask. The marker 455
indicates the value of the spectrum that is closest to the frequency
mask, and the marker 460 indicates the corresponding value of the
frequency mask.

[0015] In another embodiment, the trigger event detector 305 is a "density
trigger" as described in co-pending U.S. application Ser. No. 12/568,141
titled "Frequency Domain Bitmap Triggering Using Color, Density and
Correlation Based Triggers" which generates a trigger signal when the
sample density within a user-defined density marker box exceeds a
user-specified density threshold. In that case, the processed digital
samples are the instantaneous density within the density marker box and
the user-specified trigger threshold is the density threshold. The marker
455 indicates the instantaneous value of the density, and the marker 460
indicates the density threshold.

[0016] In another embodiment, the trigger event detector 305 is an
"external trigger" which generates a trigger signal when the voltage
sensed at an external trigger input connector (not shown) exceeds a
user-specified voltage threshold. In this case, the processor 345 does
not receive the processed digital samples from the trigger event detector
305, but rather receives the voltage sensed at the external trigger input
connector, and the user-specified trigger threshold is the voltage
threshold. The marker 455 indicates the instantaneous voltage sensed at
the external trigger input connector, and the marker 460 indicates the
voltage threshold.

[0017] In another embodiment, the trigger event detector 305 is a
"modulation domain trigger" as described in co-pending U.S. application
Ser. No. 11/009,161 titled "Modulation domain trigger" which transforms
the digitized samples of the signal-under-test into the modulation domain
and generates a trigger signal when an anomaly is detected. In that case,
the figure-of-merit may be any one of various signal quality measurements
such as error vector magnitude (EVM), phase error, magnitude error,
in-phase/quadrature (I/Q) imbalance, skew, origin offset, number of bits
per second, packets per second, and so on. In general, any quantifiable
aspect of the signal may be used as a figure-of-merit.

[0018] It will be appreciated that the list of trigger event detectors
described above is not an exhaustive list, and that a real-time trigger
figure-of-merit indicator may be used in conjunction with any kind of
trigger event detector now existing or yet to be developed without
departing from the spirit and scope of the invention. That is, regardless
of the particular trigger condition that a trigger event detector uses, a
real-time trigger figure-of-merit indicator can be used to provide a
real-time indication of how close a signal-under-test is to satisfying
that trigger condition. For example, if a trigger event detector
generates a trigger signal when an aspect of a signal-under-test
"matches" a specified condition (such as a specified data pattern, a
specified spectral signature, or the like), then the real-time trigger
figure-of-merit indicator may indicate "nearness of match,"
"degree-of-match," or the like. Furthermore, some types of trigger event
detectors may have more than one figure-of-merit. Multiple indicators may
be used with those types of trigger event detectors, one for each
figure-of-merit.

[0019] Although the real-time trigger figure-of-merit indicator was
described above as being used in conjunction with a spectrum analyzer, it
will be appreciated that in various other embodiments a real-time trigger
figure-of-merit indicator may be used in conjunction with any other kind
of test and measurement instrument that uses a trigger event detector
such as an oscilloscope or a logic analyzer.

[0020] Although the real-time trigger figure-of-merit indicator was
depicted in the Figures as a vertical bar, it will be appreciated that in
other embodiments the indicator may have a different visual appearance,
e.g., it may be a horizontal bar, a dial, and so on.

[0021] In various embodiments, the processor 345 may be implemented in
hardware, software, or a combination of the two, and may comprise a
general purpose microprocessor, a digital signal processor (DSP), an
application specific integrated circuit (ASIC), a field-programmable gate
array (FPGA), or the like.

[0022] It will be appreciated from the foregoing discussion that the
present invention represents a significant advance in the field of
triggers for test and measurement instruments. Although specific
embodiments of the invention have been illustrated and described for
purposes of illustration, it will be understood that various
modifications may be made without departing from the spirit and scope of
the invention. Accordingly, the invention should not be limited except as
by the appended claims.

Patent applications by John F. Turpin, Tigard, OR US

Patent applications by TEKTRONIX, INC.

Patent applications in class History logging or time stamping

Patent applications in all subclasses History logging or time stamping